1. Field of the Invention
The present invention relates to internal combustion engines and pertains particularly to improved piston and compression ring combination for reducing emissions of pollutants, and increasing engine power and efficiency.
2. Discussion of the Related Art
The reciprocating piston internal combustion engine is perhaps the most widely used engine in the world today. However, this type of engine produces many types of harmful emissions that pollute the atmosphere. A great deal of effort has gone into the reduction of these objectionable emissions. In order to find a solution, each type of pollutant is typically treated in its own special way.
One of the major polluting emissions from spark ignition engines is unburned hydrocarbons. Unburned hydrocarbons are found in the exhaust due to a portion of the inducted fuel escaping combustion and exiting the cylinder partially or completely unoxidized. Four potential sources of the unburnt fuel that results in hydrocarbon emissions are the quenching of the combustion flame away from fuel coated chamber surfaces, premature quenching of the flame due to abnormal in-cylinder conditions, absorption of fuel by the cylinder wall oil layer, and storage of air/fuel mixture in engine ring crevices too narrow for flame propagation.
Studies have discovered that out of those four hydrocarbon sources, the dominating source is unburned fuel in engine cylinder ring crevices. In each cylinder, a top ring crevice exists between the side of the piston, the cylinder wall, and the top piston ring which forms the seal between the piston and the cylinder. During engine operation, fuel in a finely atomized state is injected into a cylinder and compressed during the up stroke of the piston. The compressed mixture is then ignited creating an explosion which forces the piston down generating power. However, in engines with a typical ring configuration, some of the fuel air mixture is trapped in the top ring crevice and some of the fuel spray adheres to the relatively cooler cylinder wall in the crevice. During combustion, because the top ring crevice is too narrow for the flame to enter, the fuel air mixture and the fuel spray in the crevice is not burned as effectively as that above the piston head. As a result, part of the cylinder charge escapes the normal engine combustion process thereby producing unburned hydrocarbons and preventing that portion of fuel from being converted into engine power. Numerous studies have concluded that the impact of this flow of cylinder gases into and out of the top ring crevices, on unburned hydrocarbons and engine efficiency and power, is significant. Therefore, an engine with such ring crevices has less fuel efficiency, less power, and higher exhaust hydrocarbon emissions than an engine without the crevices.
For instance, N. Namazian and J. B. Heywood, xe2x80x9cFlow in the Piston-Cylinder-Ring Crevices of a Spark-Ignition Engine: Effect on Hydrocarbon Emissions, Efficiency and Power,xe2x80x9d SAE paper 820088, 1982, a study of the fraction of the crevice gas which is unburned, shows that depending on spark plug and ring gap location, between 4 and 8 percent of the induced fuel-air mixture escapes the primary combustion process. Between 0.5 and 1.2 percent of this percentage is blowby through a gap in the rings structure which is necessary for mounting the ring on the piston. The study further demonstrates that reduction in pistontop-land crevice-volume has a significant effect on the unburned fuel returning to the cylinder. In one SAE test engine, if the top land crevice volume is removed, a 70% reduction in hydrocarbons returning to the combustion chamber would be achieved. Similarly, J. T. Wentworth, xe2x80x9cThe Piston Crevice Volume Effect on Exhaust Hydrocarbon Emissionsxe2x80x9d, Combustion Science and Technology, Vol. 4, pp. 97-100, 1971, observes about a 50 percent reduction in exhaust hydrocarbons emissions when the total piston-cylinder crevice volume was virtually eliminated. Furthermore, the Namazian study shows that the crevice gas flow represents a significant power and efficiency loss. Depending on the degree and rate of in cylinder oxidation, and design and operating details, these losses are at least 2 to 7 percent.
Various proposals have been made to eliminate hydrocarbon emissions associated with the ring crevice. T. Saika and K. Korematsu, xe2x80x9cFlame Propagation into the Ring Crevice of a Spark Ignition Engine,xe2x80x9d SAE paper 861528, 1986, proposes a ring crevice design that has a wider clearance between the piston and cylinder into which the flame propagates in order to reduce the amount of unburnt fuel. However, by decreasing the amount of unburnt fuel air mixture, this design only partially reduces those hydrocarbon emissions associated with the ring crevice. Further, this design could diminish engine life due to the burning of piston edges. Alternatively, M. Willcock, D. H. Tidmarsh, P. Foss and D. Bates, xe2x80x9cA Comparison of Hydrocarbon Emissions from Different Piston Designs in an S1 Engine,xe2x80x9d SAE paper 930714, 1993, proposes reducing the ring crevice height by moving the top piston ring closer to the piston top in order to reduce hydrocarbon emissions. Nevertheless, this design only partly reduces hydrocarbon emissions by reducing the ring crevice 35% in volume.
In order to prevent the top of a piston from burning and to reduce friction between the piston rings and cylinder wall, U.S. Pat. No. 4,774,917, discloses an inclined piston groove with the inner part of the groove lower than its outer edges and a piston ring mounted in this groove and extending vertically to nearly the top of the piston. However, this design requires that the distance between the piston and cylinder wall be less than the width of the vertical portion of the piston ring. The resulting gap allows gasses and unburnt fuel to leak below this top ring resulting in more pollution, and less efficiency and power than a piston without this gap.
U.S. Pat. No. 5,450,783, discloses a single strip piston ring with a horizontally symmetrical cross section for engaging two grooves in a pistons upper edge. The ring has two wedge shaped legs for engaging two wedge shaped grooves in the piston. The grooves are separated so that there is a tapering protrusion created between them. During use, this tapering protrusion""s wedged shaped causes the upward and downward forces on the ring to produce a dynamic force pressing the ring against the cylinder wall. Thus, the energy required to overcome the force pressing the ring against the cylinder wall causes the piston to be less efficient and have less power than a xe2x80x9cdead ringxe2x80x9d or piston/ring design that does not create the dynamic outward ring force.
There exists, therefore, an established and significant need to reduce harmful exhaust hydrocarbon emissions from spark ignition engines without loss of power and fuel efficiency, particularly with respect to emissions resulting from unburnt fuel in engine cylinder crevices. It is therefore desirable to have an improved piston and compression ring combination with an upper flange and sealing surface exposed to combustion to reduce or eliminate cylinder crevices thereby reducing pollutant emissions, while increasing engine power and efficiency. The present invention fulfills all of these needs and provides further related advantages.
It is the primary object of the present invention to provide an improved internal combustion engine piston and compression ring construction that reduces or eliminates the crevice around the top of a piston, thereby lowering hydrocarbon emissions while increasing engine power and efficiency.
One embodiment of the invention provides a compression ring having a generally annular configuration with an upper inwardly directed flange, a radially outwardly directed sealing surface adapted to engage an inner surface of a cylinder, a downwardly depending skirt portion, and a retaining foot extending radially from a lower portion of the skirt.
A preferred embodiment of the present invention provides a compression ring having a generally annular configuration with an upper inwardly directed flange overlaying the upper end of a piston. The ring has a radially outwardly directed surface forming a seal against the inside of the engine cylinder. A downwardly depending skirt portion of the ring ends in a retaining foot that extends radially inward engaging an annular groove around the outside of the piston.
Another embodiment provides an improved piston ring construction having an annular configuration with an upper inwardly directed flange overlaying the upper end of a piston, an outwardly directed sealing flange, and a downwardly depending skirt portion ending in a retaining foot that is extended into a groove in the upper surface of the piston.